1. Field of the Invention
The present invention is related to an optical scanning device used to carry out record formation of an electrostatic latent image on the photo conductive surface which is a surface to be scanned, a control method of the optical scanning device, and an image forming apparatus using the optical scanning device.
2. Description of the Related Art
An optical scanning device used for a laser printer or a like scans a surface to be scanned such as a photosensitive drum by light flux such as a laser beam by using an optical deflector such as a polygon mirror and an image optical element such as an Fθ lens, and forms an image. Conventionally, various technologies have been disclosed to suppress an imaging misalignment from the surface to be scanned.
There are cases in which the imaging misalignment can be caused by an optical path difference for each scanning angle in one scan execution between a starting side and a terminating side, in which a different imaging misalignment can be caused for each scan corresponding to a reflection surface accuracy of the polygon mirror, and in which the imaging misalignment can be caused with age by a change of a lens size or a laser wavelength by variations in environmental temperature. The optical path difference is a difference of a distance between optical elements such as lenses, or a difference caused by an optical path being changed due to a varied lens effect after being deflected by the polygon mirror.
Japanese Laid-open Patent No. 2004-109782 discloses to adjust a beam imaging position by changing a focal length of a variable focus optical element so as to correct an influence caused by an accuracy dispersion of a deflecting reflection face of the polygon mirror.
Japanese Laid-open Patents No. 2002-244063 and No. 2007-102108 disclose to correct the imaging misalignment due to temperature, by changing the focal length of the variable focus optical element in response to a detected temperature.
However, in the above described technologies, there is no effect to reduce the imaging misalignment corresponding to a scan angle since the focal length of the variable focus optical element is not changed in one scan execution.
Japanese Laid-open Patent No.59-62821 discloses that a perpendicular returning part is provided by arranging a mirror on an optical path, and a position of a focal point in a scan operation is changed by changing an optical path length by vibrating the mirror in a direction perpendicular to an optical path. However, the optical path becomes complex. Moreover, since the mirror is mechanically moved, accuracy is lower and a high speed response is significantly limited in practice.